1. Field of the Invention
The present invention relates to a laminated electronic component and a method of producing the same, and more particularly, to a laminated electronic component in which an external terminal electrode connected with an internal conductor is formed through a step of direct plating on an outer surface of an electronic component body.
2. Description of the Related Art
Recently, the market for small-sized portable electronic instruments, such as mobile phones, notebook personal computers, digital cameras, and digital audio instruments has been expanding. In such portable electronic instruments, not only is the size getting smaller, but also the performance is getting higher. Such a portable electronic instrument is equipped with a plurality of laminated ceramic electronic components, and smaller size and higher performance are also desired for these laminated ceramic electronic components. In a laminated ceramic capacitor, for example, smaller size and larger capacity are desired.
As an approach to achieve smaller size and larger capacity of the laminated ceramic capacitor, it is effective to reduce the thickness of the ceramic layer, and a capacitor having a ceramic layer with a thickness of about 3 μm or less has recently been developed. Presently, a further reduction in the thickness of the ceramic layer has been attempted. However, when the thickness of the ceramic layer is further reduced, a short circuit between internal electrodes is likely to occur.
As another approach, it is effective to increase an effective area of an internal electrode. However, in mass production of a laminated ceramic capacitor, a side margin between an internal electrode and a lateral surface of a ceramic base material and an end margin between an internal electrode and a ceramic base material end surface should be maintained to account for misalignment during the lamination of ceramic green sheets and misalignment during cutting. Therefore, when an effective area of an internal electrode is increased, it is necessary to increase the area of the ceramic layer so as to provide predetermined margins. However, there is a limit to the amount that the ceramic layer can be increased within a specified dimensional standard of the product, and the thickness of the external terminal electrode will prevent further increases in the area of the ceramic layer.
Conventionally, an external terminal electrode of a laminated ceramic capacitor is formed by applying and firing a conductive paste on a ceramic base material end portion. As a method for applying a conductive paste, it is conventional to dip a ceramic base material end portion into a paste vessel, followed by lifting it out of the paste vessel. However, with this method, the conductive paste is likely to be thicker in a central portion of the ceramic base material end surface due to the influence of viscosity of the conductive paste. Therefore, the thickness of the external terminal electrode partially increases, e.g., to greater than 30 μm, and it is not possible to sufficiently reduce the volume of the ceramic base material.
In response to this problem, a method of forming an external terminal electrode by direct plating has been proposed. According to this method, a plating film precipitates on an exposed portion of an internal electrode in a ceramic base material end surface as a nucleus, and the exposed portions of the neighboring internal electrodes are connected to each other as a result of growth of the plating film. According to this method, it is possible to form a thinner and flatter electrode film as compared to the conventional method using a conductive paste (see, for example, International Patent Publication No. 2007/049456).
However, when forming an external terminal electrode on the outer surface of an electronic component body, i.e., a ceramic base material, by direct plating, when an average grain diameter of metal grains in a plating film used to form the external terminal electrode is increased, a problem arises in that water enters through a gap between the electronic component body and the plating film. Further, when the thickness of the plating film is reduced, there is a problem in that the continuity of the plating film is deteriorated due to a reduced smoothness of the plating film. In these cases, there is a problem in that reliability is decreased, for example, the insulation resistance is decreased over time.